Take a HARD look at what Beaver says, especially when you have rebuilt an engine, the zinc compounds in the oil protect the flat surfaces, specifically, zinc is an anti-wear additive for surfaces such as tappets and cams. The zinc has been lower, lowered, gone out of most oils now. As an engine wears, it uses oil, and zinc degrades the catalytic converter performance so big brother required they phase it out. It is still found in Rotella diesel type oils as well as the "high Mileage" blends and in certain additives. Do not take my word on this...do some research on the net, I will post some websites so you can check this out. Anyway, diesels are going to have catalytic converters soon, so the zinc will be gone from them also. The GM EOS assembly lube is a MUST when starting up a new engine, cams usually go flat pretty quick. No more time now, I will leave the info for you to make up your own mind.
http://www.hotrod.com/techarticles/engine/flat_tappet_cam_tech/oil_summary.html http://www.bobistheoilguy.com/motoroil.html#ZINC heres the better article:
http://www.hotrod.com/techarticles/engine/flat_tappet_cam_tech/index.html
